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S A Newman

Publications and source records attributed to S A Newman.

At least 19 recordsLinked to original sources
PubMed2005

On multiscale approaches to three-dimensional modelling of morphogenesis.

In this paper we present the foundation of a unified, object-oriented, three-dimensional biomodelling environment, which allows us to integrate multiple submodels at scales from subcellular to those of tissues and organs. Our current implementation combines a modified discrete model from statistical mechanics, the Cellular Potts Model, with a continuum reaction-diffusion model and a state automaton with well-defined conditions for cell differentiation transitions to model genetic regulation. This environment allows us to rapidly and compactly create computational models of a class of complex-developmental phenomena. To illustrate model development, we simulate a simplified version of the formation of the skeletal pattern in a growing embryonic vertebrate limb.

Animals↗
PubMed2004

CompuCell, a multi-model framework for simulation of morphogenesis.

MOTIVATION: CompuCell is a multi-model software framework for simulation of the development of multicellular organisms known as morphogenesis. It models the interaction of the gene regulatory network with generic cellular mechanisms, such as cell adhesion, division, haptotaxis and chemotaxis. A combination of a state automaton with stochastic local rules and a set of differential equations, including subcellular ordinary differential equations and extracellular reaction-diffusion partial differential equations, model gene regulation. This automaton in turn controls the differentiation of the cells, and cell-cell and cell-extracellular matrix interactions that give rise to cell rearrangements and pattern formation, e.g. mesenchymal condensation. The cellular Potts model, a stochastic model that accurately reproduces cell movement and rearrangement, models cell dynamics. All these models couple in a controllable way, resulting in a powerful and flexible computational environment for morphogenesis, which allows for simultaneous incorporation of growth and spatial patterning. RESULTS: We use CompuCell to simulate the formation of the skeletal architecture in the avian limb bud. AVAILABILITY: Binaries and source code for Microsoft Windows, Linux and Solaris are available for download from http://sourceforge.net/projects/compucell/

Animals↗
PubMed2003

Quadriceps voluntary activation at different joint angles measured by two stimulation techniques.

People are able to fully activate their quadriceps at mid-length during a brief isometric contraction but it is uncertain whether this is the case at other muscle lengths. With the twitch superimposition technique for determining levels of voluntary activation (VA), the muscle may be stimulated through the intramuscular branches of the nerve or via the nerve trunk itself. The former technique is easier to use, but different populations of motor units may be stimulated if the joint position is changed to alter muscle length. The purpose of this study was to investigate quadriceps VA at a range of knee joint angles using both magnetic stimulation of the motor nerve and percutaneous electrical stimulation over the muscle belly. Eight healthy subjects (six females, mean age 29 years) performed maximal voluntary contractions of the quadriceps at knee joint angles at 10-110 degrees of flexion. Surface electromyography (EMG) of quadriceps and hamstrings was recorded as an indication of the amount of muscle activity. Nearly all subjects showed >95% VA at all joint angles. VA did not vary with joint angle nor were there significant differences between the two stimulation techniques. Similarly, there was no significant effect of knee joint angle on the EMG activity of either muscle group. These findings indicate that VA of the quadriceps during a brief isometric contraction is not affected by muscle length and can be measured by either stimulation technique.

Adult↗
PubMed2001

Cranioorbital fibrous dysplasia: with emphasis on visual impairment and current surgical management.

Fibrous dysplasia is a benign but slowly progressive disorder of bone in which normal cancellous bone is replaced by immature woven bone and fibrous tissue. Significant deformity and both acute and chronic visual impairment can result. A contemporary understanding of fibrous dysplasia, emphasizing the origins of visual impairment, indications for decompressive surgery, and the techniques for correction of the cosmetic deformity are presented. In their experience and review of the literature, the authors found the most frequent clinical presentations to be exophthalmos, displacement of the globe, abnormalities of extraocular motility, cosmetic deformity, and visual impairment. Although traditionally the cause of visual impairment has been ascribed to impingement of the optic canal on the optic nerve, the authors' experience is that the most common cause of visual loss is cystic degeneration of the tumor, particularly with those involving the anterior clinoid process. Exophthalmos and optic canal stenosis are less common causes of visual impairment. Indications for surgical intervention include acute and/or serially radiographically documented and relentless visual impairment and significant cosmetic deformity. Individualized management strategies are also discussed.

Adolescent↗
PubMed2001

Abdominal muscle activity during the abdominal hollowing manoeuvre in the four point kneeling and prone positions.

This study investigated the pattern of recruitment of the abdominal muscles during the abdominal hollowing manoeuvre (AHM), in four point kneeling and prone. Muscle activity was detected and recorded by surface electromyography (EMG), in 20 healthy subjects, 8 male and 12 female, aged between 19 and 30 during both maximal activity, and the AHM. The degree of activation during hollowing was expressed as a percentage of maximal. There was activity in the internal abdominal oblique (IO) during all hollowing manoeuvres, in both starting positions, whilst only two subjects showed any activity in rectus abdominis (RA). Simultaneous activity in IO and EO occurred both in four point kneeling (45% of the subjects) and especially in prone (75% of the subjects). Across both positions IO activity was significantly greater than EO. There was no significant difference in EO or IO activity comparing across positions. These results suggest that the AHM when performed in four point kneeling and prone always activates IO and rarely activates RA, whilst elimination of activity in EO is more difficult to achieve, particularly in prone. Isolated activity in the deep abdominal muscles may not always be achievable in these starting positions.

Abdominal Muscles↗
PubMed2000

Epigenetic mechanisms of character origination.

The close mapping between genotype and morphological phenotype in many contemporary metazoans has led to the general notion that the evolution of organismal form is a direct consequence of evolving genetic programs. In contrast to this view, we propose that the present relationship between genes and form is a highly derived condition, a product of evolution rather than its precondition. Prior to the biochemical canalization of developmental pathways, and the stabilization of phenotypes, interaction of multicellular organisms with their physicochemical environments dictated a many-to-many mapping between genomes and forms. These forms would have been generated by epigenetic mechanisms: initially physical processes characteristic of condensed, chemically active materials, and later conditional, inductive interactions among the organism's constituent tissues. This concept, that epigenetic mechanisms are the generative agents of morphological character origination, helps to explain findings that are difficult to reconcile with the standard neo-Darwinian model, e.g., the burst of body plans in the early Cambrian, the origins of morphological innovation, homology, and rapid change of form. Our concept entails a new interpretation of the relationship between genes and biological form.

Animals↗
PubMed2000

Stages of improvement in visual fields after pituitary tumor resection.

PURPOSE: To use static threshold perimetry to examine the stages of improvement and the potential for late improvement of visual fields after surgical resection of pituitary adenomas causing visual loss from compression of the anterior visual pathways. METHODS: Retrospective review of charts of patients with pituitary tumors and abnormal static threshold perimetry before or soon after treatment who had subsequent visual fields. Quantification of the visual field mean deviation overall, superotemporally, and inferotemporally was performed and compared between visits. Postoperative visits were considered in five time periods: visit 1 (surgery to 1 week), visit 2 (1 month to 4 months), visit 3 (6 months to 1 year), visit 4 (2 years), and visit 5 (3 or more years). RESULTS: Sixty-two patients were included (33 men and 29 women; mean age 54 years [SD +/- 15 years; range, 22 to 83 years]). At visit 1, the relative improvement of the overall mean deviation for the right eye was 30.8% (P =.01) and for the left eye was 13.7% (P =.3067). At visit 2, the relative improvement of the overall mean deviation for the right eye was 30. 4% (P =.0142) and for the left eye was 32.6% (P =.0092). At visits 1 and 2, the inferotemporal quadrants were the quadrants with greatest improvement (visit 1, right eye, 37.8% [P =.0082]; visit 2, left eye, 30.8% [P =.0074]). At visits 3, 4, and 5, an overall trend toward mild improvement was observed with statistical significance only for the inferotemporal quadrant of the left eye from visit 2 to visit 3, which improved 19.7% (P =.0270). CONCLUSION: The pattern of recovery of visual function after decompression of the anterior visual pathways suggests at least three phases of improvement. The early fast phase (surgery to 1 week) of improvement may lead to normalization of visual fields in some individuals. The early slow phase (1 month to 4 months) is the period of most notable improvement. A late phase (6 months to 3 years) of mild improvement does not appear significant overall but may be marked in some individuals. Each of these phases may have one or more mechanisms underlying the observed improvement.

Adenoma↗
PubMed2000

Heart rate as a predictor of future blood pressure in schoolchildren.

Heart rate (HR) has been shown to predict future blood pressures (BP) in studies in adults. We explored the relation of HR to future BP levels in a cohort of 344 black and 456 white schoolchildren ages 5 to 19 years, to examine the hypothesis that HR predicts subsequent BP even very early in life. After making baseline measurements, BP was assessed longitudinally 1 to 24 additional times (mean = 8.25) after the baseline period, at intervals of approximately 6 months. We found that HR was significantly related to future diastolic BP in the black boys (P = .016) after adjusting for baseline diastolic BP, age, and body mass index, but not in the black girls or in the white children. Because HR is reflective of sympathetic nervous system (SNS) activity that in turn can be related to the renin-angiotensin system (RAS), we also explored the relation of HR to the RAS by studying relationships to variants in the angiotensinogen gene and the angiotensin I-converting enzyme (ACE) gene. We found a significantly positive relationship of HR to the presence of the deletion allele of the ACE gene (P = .0015), but, again, only in the black boys. Because blacks in general appear to retain additional sodium when compared with whites, the SNS, as reflected in the HR, may influence BP more when individuals have increased sodium retention. In summary, baseline HR predicted future diastolic BP in the black boys but not in the black girls or in the white children.

Adult↗
PubMed1999

Generation, integration, autonomy: three steps in the evolution of homology.

The homology concept harbours implicit assumptions about the evolution of morphological organization. Homologues are natural units in the construction of organismal body plans. Their origin and maintenance should represent a key element of a comprehensive theory of morphological evolution. Therefore, it is necessary to understand the causation of homology and to investigate the mechanisms underlying its origination. The study of this issue cannot be limited to the molecular level, because there appears to exist no strict correspondence between genetic and morphological evolution. It is argued that the establishment of homology follows three distinct (if overlapping) steps: (a) the generation of morphological building elements; (b) the integration of new elements into a body plan; and (c) the autonomization of integrated construction units as lineage-specific homologues of phenotypic evolution. In contrast with traditional views, it is proposed that the mechanistic basis for steps (a) and (b) is largely epigenetic, i.e. a consequence of the inherent propensities of developmental system under changing conditions. Step (c) transcends the proximate mechanisms underlying the establishment of homologues and makes them independent attractors of morphological organization at the phenotypic level.

Anatomy, Comparative↗
PubMed1999

Levels of mineralocorticoids in whites and blacks.

Blacks appear, on average, to retain more Na than whites. A higher production rate of mineralocorticoids could explain the greater Na retention in blacks. Although production of aldosterone has been shown to be lower in blacks, the level of another mineralocorticoid may be increased. Plasma levels of deoxycorticosterone and cortisol were measured in young whites (n=23; age=16.4+/-3.1[SD] years) and young blacks (n=25; age=13.8+/-1.3 years). Blacks had lower plasma levels of renin activity and aldosterone and lower urinary aldosterone excretion rates; thus, they appeared to be representative of blacks that retain additional Na. Plasma deoxycorticosterone levels were lower in blacks than in whites both at baseline (247+/-161 versus 381+/-270 pmol/L, P=0.048) and after stimulation with adrenocorticotropic hormone (822+/-294 versus 1127+/-628 pmol/L at 30 minutes, P=0.047; 925+/-366 versus 1440+/-834 pmol/L at 60 minutes, P=0.013). Cortisol levels were also lower in blacks at baseline (P=0.014) but were not significantly different from levels in whites after stimulation with adrenocorticotropic hormone. In a larger cohort of 407 whites (age=12.0+/-2.9 years) and 247 blacks (age=12.9+/-3.1 years), 18-hydroxycortisol excretion rates were also lower in blacks (P=0. 021). In conclusion, increased Na retention in blacks does not appear to be secondary to increased production of either aldosterone, deoxycorticosterone, cortisol, or 18-hydroxycortisol. A primary renal mechanism may mediate the increase in Na reabsorption in blacks.

Adolescent↗
PubMed1999

The cavernous sinus.

The parasellar region, in particular the cavernous sinus, represents the confluence of critical structures involved in both the afferent and efferent visual pathways. It is not surprising that lesions affecting the area of the cavernous sinus most frequently present with neuro-ophthalmic complaints, which include double vision, decreased vision, pain, and numbness. Neuro-surgical intervention in the area of hte cavernous sinus often produces neuro-ophthalmic complications. A rehabilitative effort directed to the neuro-ophthalmic manifestations is essential for patients with skull-base pathology.

Adult↗
PubMed1998

Human cloning.

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Advisory Committees↗